Specific Immune System Flashcards
Antigens
Basis of the specific immune system
Molecules found in any organism that can be recognised by antibodies and T cell receptors and stimulate an immune response
They can originate from:
- Pathogens (bacteria or viruses)
- Other organisms (e.g. pig or human transplants)
- Persons own body (e.g. in autoimmune disease)
Major Histocompatibility Complex
A molecule that sits on the surface of cells - that the cell can use to present antigens to T-Cells
Specifically, in humans this molecule can be called HLA (human leukocyte antigen)
Many shapes that this moleucle can take - each human having their own specific shape of MHC coded for by over 100 genes
- Reason for transplant rejection
- Closer the MHC type is to the donor the less likely the organ will be to being rejected
2 types of MHC/HLA molecules:
- Class 1
- Class 2
Class 1 MHC molecules:
- Found on all cells with a nucleus
- Presents antigens that come from within the cells (i.e. from a virus that has infected and is replicating within the cells)
- Recognised exclusively by CD8 cells
- This allows CD8 cells to recognise almost any cell that has been infected with an organism to destroy it
Class II MHC Molecules:
Found mostly on:
- Dendritic cells macrophages monocytes and B-cells
Presents antigens that come from outside the cell (cells pick up material from outside the cell, digest it and present the antigens on the Class II MHC molecules)
- Recognised exclusively by CD4 cells
- Allows relevant immune cells that have come into contact with pathogenic material to transport it and present it to CD4 cells which the respond and become T-Helper cells
- You wouldn’t want CD8 cells to recognise this as it would lead to destruction of non-infected cells
CD4 activation
The first step in the activation of the specific immune system
- Done by dendritic cells which present pathogenic material on their HLA II molecules
- Dendritic cells enter either/or:
—- Paracortex in the lymph node
—- PALS in the spleed
in search for relevant CD4 cells
CD4 after activation
- Massive proliferation (stage lasts a few days)
- They then differentiate into T-Helper cells
2 types of T helper cells (Th1/Th2)
- They release different cytokines and play different roles
Both Th1/2 cells are responsible for stimulating B cells
- Displaying the antigen on their HLA II molecules to proliferate and differentiate by releasing cytokines
- Antibody class they differentiate into depends on the type of T-helper cell
Th1 (T-helper 1) responsible for:
- Stimulate B cells to produce IgG
- Secreting IL-2 – which stimulates the proliferation and differentiation of other CD4 and CD8 cells
- They play an important role in CD8 cells recognizing antigen, proliferating, and differentiating into cytotoxic T cells
- They travel to the site of the infection and release cytokines that stimulate the recruitment and differentiation of monocytes into macrophages, and the activation of the macrophages
- —- This is called “DELAYED TYPE HYPERSENSITIVITY REACTION” or Type IV hypersensitivity reactions
Th2 cells are responsible for:
- Stimulating B cells to produce all antibodies, but notably more IgE
- Travelling to site of infection and releasing cytokines that stimulate the recruitment and activation of mast cells and eosinophils
- Th2 cells are important in parasitic infections and in Type 1 hypersensitivity reactions (allergy) and asthma
Cytotoxic T-Cells
- Differentiated from CD8 cells
- — Triggered by T helper cells and dendritic cells with HLA I protein presenting
- Essential to destroy cells that have been invaded
Destroy infected cells by 2 mechanisms:
1) Granule exocytosis:
- - Enyzymes are released that cause cell lysis and death
2) Apoptosis:
- - By activating Fas molecule in cell
5 Different classes of Immunoglobulins/ Antibodies:
IgA - Secreted in mucous (Come in pairs)
IgD - Found on B cell membranes, unstable and doesn’t last long when secreted into blood
IgE - Found in low levels in blood, important in asthma and allergy (measuring specific IgE to allergens can give good indication about persons allergy status)
IgG - Most common antibody in blood, useful marker of immunity
IgM - First antibody produced in acute infection, measuring can give a good indication of acute infection
— Has snowflake appearance (5 molecules)
B Cells:
B cells use antibodies on their surface membrane to recognise antigens from pathogens
- These antibodies are either IgM (Most often) or IgD
- Each B cell only has antibodies to a specific antigen
- B cells sit in lymph nodes, spleen or MALT and pick up antigens that are specific to their antiboides
- they then process that antigen and present it on their HLA II molecules
- T helper cells that are specific to that antigen can then recognise them and will be stimulated to produce cytokines that activate the B cell
- Once activated by antigen/ t-helper cells, they undergo differentiation and become either:
1) Plama cells
2) Memory B cells
In the germinal centres of the lymph nodes, spleen and malt
Where do B cells undergo differentiation:
Germinal centres of the lymph nodes, spleet or MALT
IgA
IgA
This is heavily secreted in mucous to protect mucous membranes from infection, such as in saliva, respiratory secretions and breast milk.
In blood it has the simple Y structure.
In secretions it the Ys attach at the Fc portion in pairs.
IgD
IgD
IgD is found on B cell membranes, and is unstable and doesn’t last long when secreted into the blood.
IgE
IgE
IgE is found in only low levels in the blood.
In the blood it has a simple Y structure.
It is important in asthma and allergy, and measuring specific IgE to allergens (e.g. peanuts) can give an indication about a person’s allergy status.
